This invention relates to a rotational viscometer apparatus and a process utilizing the same for measuring the viscosity of a fluid medium; and more particularly to an apparatus and process capable of approximating the true viscosity of non-Newtonian fluids.
Various techniques are known in the art for the repetitive or continuous measurement of the viscosity of Newtonian fluids, and a number of such arrangements are described in the introductory portion of U.S. Pat. No. 3,875,791, the invention of which relates to a rotary viscometer capable of providing a true indication of the viscosity of Newtonian fluids, and of characterizing a fluid as to its Newtonian or non-Newtonian character.
The rotary viscometer of U.S. Pat. No. 3,875,791, rotates a fluid shearing spindle in a cup containing the fluid to be characterized, at a rotation speed which can be scanned across a desired range; and provides a plot of fluid shearing torque to which the spindle is subjected, as a function of spindle rotation speed. If the torque increases linearly with speed, the fluid is Newtonian, with a viscosity equal to the torque/speed ratio. If the torque variation with speed is non-linear, the fluid is non-Newtonian.
While the rotary viscometer arrangement of U.S. Pat. No. 3,875,791 is thus quite accurate and useful in connection with Newtonian fluids, it is incapable of directly providing true viscosity information for non-Newtonian fluids. For such non-Newtonian fluids, an effective differentiation of the torque-speed curve is required, since the true viscosity of the non-Newtonian fluid at any given spindle rotation speed is proportional to the slope of the torque-speed curve at such speed.
Accordingly, an object of the present invention is to provide an improved rotary viscometer which is capable of not only generating torque vs. spindle rotation speed curves, but also of generating information respecting the approximate true viscosity of non-Newtonian fluids.